Increased β-Endorphin Levels and Generalized Decreased Pain Thresholds in Patients With Limited Jaw Opening and Movement-Evoked Pain From the Temporomandibular Joint

PurposePatients with limited jaw opening and movement-evoked pain from the temporomandibular joint have moderate to severe pain that may be relieved by surgery. The purpose of this study was to investigate if the preoperative state is associated with alterations in plasma β-endorphin (βE) levels and pain thresholds.Patients and MethodsEighteen female patients with painful unilateral temporomandibular joint and 18 age-matched healthy women participated. After blood sampling for analysis of plasma βE levels, pressure pain thresholds over the masseter muscles and index fingers were recorded with an electronic algometer. Electrical detection and pain thresholds were recorded with the PainMatcher (Cefar Medical AB, Lund, Sweden) device. Nonparametric statistics, ie, Mann-Whitney U test and Spearman correlation test, was used for statistical analyses.ResultsThe patients showed higher plasma βE levels (P = .013) and lower pressure pain thresholds over the masseter muscle at the painful side (P = .041) and bilaterally over the index fingers compared with the controls (P < .05 for all comparisons). High plasma βE levels correlated to increased electrical detection thresholds (n = 36, r = 0.347, P = .038).ConclusionsThis study showed that patients with limited jaw opening and movement-evoked pain from the temporomandibular joint had significantly higher plasma βE levels and lower pressure pain thresholds in the orofacial area and at remote sites compared with pain-free, healthy, age-matched controls. An increased level of βE seems insufficient to inhibit pain and central sensitization. Further studies are warranted to elucidate the relation between βE and pain thresholds secondary to stress, inflammation, and discectomy.